1. Field of the Invention
The present invention relates to a discrimination apparatus for discriminating symbols and/or characters affixed to samples, and more particularly, to a symbol/character discrimination apparatus for samples for discriminating identification symbols, characters, etc. which are formed in indentation patterns on the surface of a sample, such as a semiconductor wafer.
2. Description of the Related Art
Generally, in a process for manufacturing semiconductor devices on a semiconductor wafer (hereinafter referred to simply as wafer), a pattern such as Arabic numerals or bar codes is affixed to a predetermined position on the wafer in order to facilitate discrimination or management of the type of the wafer, manufacturing process, etc. A measuring light beam is applied to the pattern, and a reflected light beam from the patterns is landed on image sensing means, such as a CCD camera. The pattern, thus recognized as images, is compared with the previously stored patterns for identification, so that the wafer quality and process management can be checked as the semiconductor devices and manufactured.
The aforesaid patterns include, for example, engraving characters or dot characters, cut continuously or in dots with use of a laser beam, and characters formed of combinations of fine strips extending at 45.degree. to an incident laser beam. Among these patterns, the cut patterns vary considerably in cut depth according to purposes, including ones as deep as several micrometers to more than ten micrometers and ones as shallow as 1 to 2 .mu.m. The deep patterns with the cut depth of several micrometers to more than ten micrometers are subjected to a light-field measurement such that a groove portion can be recognized as a dark image contrasted by a light picture, by applying a light beam from a light source to the cutting surface of the wafer substantially at right angles thereto (light-field irradiation). This is done because reflected light beams from the groove scatter due to the irregularity of the bottom surface of the groove, and ones from the other surface region, which is specular, are regular and more abundant. If the cut groove is as shallow as 1 to 2 .mu.m, however, there is only a small difference between the amount of the scattered light beams from the bottom surface of the groove and that of the reflected light beams from the specular surface of the wafer. Accordingly, in this case, the groove portion cannot be definitely discriminated from the specular surface region.
Conventionally, therefore, a dark-field measurement is conducted in the following manner. As shown in FIG. 1, a light beam from a light source a is diagonally applied to the surface of a wafer b at a predetermined incidence angle .theta.. Then, a groove d is recognized as a region brighter than its surrounding region in a manner such that a reflected light beam in a position deviated at a small angle .theta..sub.1 from an optical axis c just opposite to that of the light source a is received, and that regularly reflected light beams from the surrounding region are not received. For securer prevention of the reception of the regularly reflected light beams, in this case, a screen plate e is disposed between the light source a and the reception side.
In the conventional discrimination apparatus of this type, however, the light source a is a single light beam emitting structure. Therefore, the light beam cannot be uniformly applied to the sample surface in the dark-field measurement, and it is difficult to discriminate the groove portion definitely from the specular portion outside the groove. Since an intricate optical system, including a lens and a mirror, is arranged between the light source a and image sensing means, moreover, the apparatus has a large size as well as a complicated construction, so that space cannot be effectively utilized. It is not very practical, therefore, to incorporate the discrimination apparatus of this type in a wafer inspection apparatus, such as a probe apparatus.